What are the rates of ventricular arrhythmias associated with isoproterenol (Isoprenaline)?

From the Guidelines

Isoproterenol increases the risk of ventricular arrhythmias, particularly in patients with pre-existing cardiac disease, and should be used with caution and continuous cardiac monitoring. When administered, isoproterenol typically increases the heart rate by 20-25% above baseline and can precipitate ventricular arrhythmias in 5-15% of patients, with higher rates in those with pre-existing cardiac disease 1. The standard dosing of isoproterenol for cardiac testing is 1-5 mcg/min IV, titrated to achieve the desired heart rate response.

Some key points to consider when using isoproterenol include:

• The arrhythmogenic potential is dose-dependent and particularly concerning in patients with structural heart disease, ischemic heart disease, or electrolyte abnormalities 1.
• Isoproterenol works by stimulating beta-1 and beta-2 adrenergic receptors, increasing heart rate, contractility, and conduction velocity through the AV node, which can trigger automaticity in ventricular tissue.
• When using isoproterenol, have resuscitation equipment readily available and consider pre-treatment with beta-blockers in high-risk patients.
• Alternative agents with lower arrhythmogenic potential should be considered for patients with known ventricular arrhythmias or structural heart disease.
• Contraindications to the administration of isoproterenol include ischaemic heart disease, uncontrolled hypertension, left ventricular outflow tract obstruction, and significant aortic stenosis, and caution should be used in patients with known arrhythmias 1.

From the FDA Drug Label

Isoproterenol may induce cardiac arrhythmias and myocardial ischemia in patients, especially patients with coronary artery disease, or cardiomyopathy. The following adverse reactions have been associated with use of isoproterenol... Cardiovascular: Tachycardia, tachyarrhythmias, palpitations, angina, ventricular arrhythmias, Adams-Stokes attacks, pulmonary edema Overdosage of isoproterenol can cause tachycardia or other arrhythmias, palpitations, angina, hypotension, or hypertension.

The rates of ventricular arrhythmias with isoproterenol are not explicitly quantified in the provided drug labels. However, ventricular arrhythmias are listed as a potential adverse reaction and a contraindication for the use of isoproterenol, indicating that they can occur in patients receiving this medication 2, 2, 2.

From the Research

Rates of Ventricular Arrhythmias with Isoproterenol

• The effects of isoproterenol on ventricular arrhythmias have been studied in various patient populations 3, 4, 5.
• In patients with Brugada syndrome, low-dose isoproterenol infusion has been shown to suppress arrhythmic storms or repetitive ventricular arrhythmias 3.
• In patients with inducible sustained ventricular tachyarrhythmias, isoproterenol infusion can reinduce the arrhythmia in some patients, identifying a subgroup at high risk of subsequent arrhythmic events 4.
• Isoproterenol has also been shown to affect sustained ventricular tachycardia circuits, shortening the VT cycle length and altering conduction within the circuit 5.
• The use of isoproterenol in diagnostic protocols, such as head-up tilt testing, has been evaluated, with a low-dose isoproterenol infusion protocol showing good diagnostic accuracy and reproducibility 6.
• Isoproterenol has also been compared to atropine in terms of its effects on inducibility of atrioventricular nodal reentrant tachycardia, with isoproterenol yielding higher inducibility rates 7.

Mechanisms and Effects

• Isoproterenol's effects on ventricular arrhythmias are thought to be related to its beta-adrenergic stimulatory properties, which can alter cardiac conduction and refractoriness 3, 5.
• The drug can shorten the QT interval, ventricular effective and functional refractory periods, and VT cycle length, making it a useful tool for diagnosing and treating certain types of ventricular arrhythmias 5.
• However, isoproterenol can also reinduce arrhythmias in some patients, highlighting the need for careful patient selection and monitoring 4.

Clinical Implications

• The use of isoproterenol in the diagnosis and treatment of ventricular arrhythmias requires careful consideration of the patient's underlying cardiac condition and the potential risks and benefits of the drug 3, 4, 5.
• Isoproterenol may be a useful adjunct to other diagnostic and therapeutic strategies, such as head-up tilt testing and radiofrequency ablation 6, 7.